The present invention relates to manufacturing semiconductor devices and, more particularly, to an improved semiconductor device comprising silicon on insulator (SOI) technology.
An important aim of ongoing research in the semiconductor industry is increasing semiconductor performance while decreasing power consumption in semiconductor devices. Planar transistors, such as metal oxide semiconductor field effect transistors (MOSFET) are particularly well suited for use in high-density integrated circuits. As the size of MOSFET and other devices decrease, the dimensions of source drain regions, channel regions, and gate electrodes of the devices, also decrease.
The design of ever-smaller planar transistors with short channel lengths makes it necessary to provide very shallow source/drain junctions. Shallow junctions are necessary to avoid lateral diffusion of implanted dopants into the channel, since such diffusion disadvantageously contributes to leakage currents and poor breakdown performance. Shallow source/drain junctions, with a thickness on the order of 1000 xc3x85 or less, are generally required for acceptable performance in short channel devices.
Silicon on insulator (SOI) technology allows the formation of high-speed, shallow-junction devices. In addition, SOI devices improve performance by reducing parasitic junction capacitance. Although SOI technology improves the performance of shallow-junction devices, devices that require deeper junctions do not benefit from SOI. For example, devices which are temperature sensitive or which require a deep implant perform better when formed in a bulk substrate.
In a SOI substrate, a buried oxide (BOX) film made of silicon oxide is formed on single crystal silicon, and a single crystal silicon thin film is formed thereon. Various methods for fabricating such SOI substrates are known. One such method is Separation-by-Implanted Oxygen (SIMOX), wherein oxygen is ion implanted into a single crystal silicon substrate to form a buried oxide (BOX) film.
Another method of forming a SOI substrate is wafer bonding, wherein two semiconductor substrates with silicon oxide surface layers are bonded together at the silicon oxide surfaces to form a BOX layer between the two semiconductor substrates.
Another SOI technique is Smart Cut(copyright), which also involves bonding semiconductor substrates through oxide layers. In the Smart Cut(copyright) method, one of the semiconductor substrates is doped with hydrogen ions prior to bonding. The hydrogen ion doping subsequently allows the hydrogen ion doped substrate to be split from the bonded substrates leaving behind a thin layer of silicon on the surface.
Strained silicon technology also allows the formation of higher speed devices. One method of forming strained-silicon transistors is by depositing a graded layer of silicon germanium (SiGe) on a bulk silicon wafer. A thin layer of silicon is subsequently deposited on the SiGe. The distance between atoms in the SiGe crystal lattice is greater than the distance between atoms in an ordinary silicon crystal lattice. Because there is a natural tendency of atoms inside different crystals to align with one another when one crystal is formed on another crystal, when silicon is deposited on top of SiGe the silicon atoms tend to stretch or xe2x80x9cstrainxe2x80x9d to align with the atoms in the SiGe lattice. Electrons in the strained silicon experience less resistance and flow up to 80% faster than in ordinary crystalline silicon.
The term semiconductor devices, as used herein, is not to be limited to the specifically disclosed embodiments. Semiconductor devices, as used herein, include a wide variety of electronic devices including flip chips, flip chip/package assemblies, transistors, capacitors, microprocessors, random access memories, etc. In general, semiconductor devices refer to any electrical device comprising semiconductors.
There exists a need in the semiconductor device art for a device that combines the performance improvements of SOI technology and strained silicon technology. There exists a need in this art to provide a semiconductor device that comprises forming strained silicon layers without forming a SiGe lattice on the substrate.
These and other needs are met by embodiments of the present invention, which provide a semiconductor device comprising a semiconductor substrate and a layer of compressive material on the semiconductor substrate. A layer of strained silicon is formed on the layer of compressive material.
The earlier stated needs are also met by certain embodiments of the instant invention which provide a method of forming a semiconductor device with a strained silicon layer comprising providing a semiconductor substrate and forming a layer of compressive material on the substrate. A strained silicon layer is subsequently formed over the layer of compressive material.
This invention addresses the needs for an improved high-speed semiconductor device with improved electrical characteristics.